The present invention relates to a pattern forming method.
In manufacturing a semiconductor device, a photolithographic technique is adopted to form a circuit pattern on a wafer. In a procedure for forming the circuit pattern using the photolithographic technique, a resist solution is applied onto the wafer to form a resist film, the resist film is irradiated with light to expose the resist film according to the desired circuit pattern, and a development process is performed to the resist film.
Recently, with a finer design rule of the semiconductor device, double patterning (multiple patterning) is proposed as the photolithographic technique for realizing high resolution. A hard mask process is well known as one of the double patterning techniques. In the hard mask process, a design pattern is divided into plural portions, and the resist patterning and transfer to the hard mask are performed to each divided design pattern. Finally a processed film is processed with the hard mask as an etching mask. However, cost increase becomes troublesome in the hard mask process.
A pattern forming method is proposed as a technique of performing the double patterning at low cost (for example, see Japanese patent No. 2757983). In the pattern forming method disclosed in Japanese patent No. 2757983, resist patterns are stacked, and the processed film is processed with the stacked multilayer resist patterns as the etching mask. In the pattern forming method, an insolubilized film is formed on a surface of a lower-layer resist pattern so as to prevent the lower-layer resist pattern from being dissolved in patterning an upper-layer resist.
However, in the pattern forming method disclosed in Japanese patent No. 2757983, a resist residue is likely to be generated in a sidewall portion of the lower-layer resist pattern in the region constituting a space when the patterning (development process) of the upper-layer resist is performed, unfortunately critical dimensions (CDs) of the lower-layer resist pattern are changed from desired values and accuracy became low.